• Journal of the Korean Society of Visualization
• /
• v.17 no.1
• /
• pp.85-92
• /
• 2019

Numerical visualization is conducted to confirm the variation of flow characteristics and pressure drop by the shape of channels on the cathode flow path in hydrogen fuel cells for unmanned aerial vehicles(UAVs). Generally, a light-weight fan is commonly used rather than a heavy air compressor at UAVS. However, in case of blower fan, a large pressure drop in the flow path causes the blocking of the oxygen supply to the fuel cell. Therefore, the uniformity of flow inside the cathode has to be achieved by changing the shape of the cathode. The flow channel, the duct shape, and the diameter of the fan are changed to optimize the flow path. As a result, it is confirmed that the optimal flow path can decrease the velocity difference between the center and outer flow by 1.8%. However, It should be noted that the channel size can increase the pressure drop.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.3
• /
• pp.285-291
• /
• 2012

A lot of research on the stability of nonpremixed flames has focused on the fuel-nozzle and quarl geometries. Of the work carried out, only a small amount has focused on the stability of the nonpremixed flame according to the recession distance and air-nozzle geometry. Therefore, in this study, a coaxial-diffusion-type gas burner with a swirler is designed for the systematic investigation of the combustion characteristics of a $CH_4$ flame depending on the recession distance and secondary air-nozzle geometry. 1st air is flowed through the swirler, and 2nd air is flowed through each nozzle. It is shown that the secondary air velocity greatly influences the flame length and shape. There is an optimum recession distance for each nozzle for the best combustion efficiency. In this study, it is shown that the optimized recession distance is nearly half the outer diameter of the air-supply nozzle.

• Journal of Korean Society of Environmental Engineers
• /
• v.38 no.9
• /
• pp.513-520
• /
• 2016

It is well known that volatile compounds including disinfection by-products as well as emissive dissolved gas in water can be removed effectively by air stripping. The micro-bubbles of flotation unit are so tiny as microns while the diameter of fine bubbles applied to air stripping is ranged from hundreds to thousands of micrometer. Therefore, the micro-bubbles in flotation can supply very wide specific surface area to transfer volatile matters through gas-liquid boundary. In addition, long emission time also can be gained to emit the volatile compound owing to the slow rise velocity of micro-bubbles in the flotation tank. There was a significant difference of the THMs species removal efficiency between air stripping and flotation experiments in this study. Moreover, the results of comparative experiments on the removal characteristics of THMs between air stripping and flotation revealed that the mass transfer coefficient, $K_La$ showed obvious differences. To overcome the limit of low removal efficiency of dissolved volatile compounds such as THMs in flotation process, the operation range of bubble volume concentration is required to higher than the operation condition of conventional particle separation.

• Fire Science and Engineering
• /
• v.15 no.3
• /
• pp.44-48
• /
• 2001

In this study, we analyzed the $CH_4$and $C_4$$H_{10}$ sensitivity measurement and voltage variation using catalytic type gas sensor characteristics in catalytic combustion type gas detecter sensors. Gas detector shall operate as intended when exposed for 24 hours to air having a relative humidity of 65 percent at a temperature of $20^{\circ}c$ and humidity of 85 percent at a temperature of $40^{\circ}c$. The gas detecter sensors are to be subjected to operation for 210 days in an area that has been determined to be equivalent to a typical residential atmosphere with an air velocity of 50 cm/sec. The source of energy for a gas detector sensors employing a supplementary basic circuit is energized from a seperate source of supply direct applied voltage 2.1V, 2.2V, 2.3V. As a result, it was confirmed that the relative humidity and temperature by regression each analysis, compared to the isobutane characteristic graph and methane characteristic graph by a relative humidity of 65% and 85% at a temperature($20^{\circ}c$, $40^{\circ}c$) show a similar linear pattern on the whore.

• Journal of Marine Bioscience and Biotechnology
• /
• v.15 no.2
• /
• pp.41-48
• /
• 2023

The objective of the present study was to improve the biomass productivity of newly isolated freshwater green microalga Parachlorella sp. This was accomplished by culture conditions optimization, including CO₂ concentration, superficial gas velocity, and light intensity, in 0.5 L bubble column photobioreactors. The supplied CO₂ concentration and gas velocity varied from 0.032% (air) to 10% and 0.02 m/s - 0.11 m/s, respectively, to evaluate their effects on growth kinetics. Next, to maximize the production rate of Parachlorella sp., a lumostatic operation based on a specific light uptake rate (q_e) was applied. From these results, the optimal CO₂ concentration in the supplied gas and the gas velocity were determined to be 5% and 0.064 m/s, respectively. For the lumostatic operation at 10.2 µmol/g/s, biomass productivity and photon yield showed significant increases of 83% and 66%, respectively, relative to cultures under constant light intensity. These results indicate that the biomass productivity of Parachlorella sp. can be improved by optimizing gas properties and light control as cell concentrations vary over time.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.8 no.3
• /
• pp.189-199
• /
• 2010

In a high-level waste (HLW) repository, heat is generated by the radioactive decay of the waste. This can affect the safety of the repository because the surrounding environment can be changed by the heat transfer through the rock. Thus, it is important to determine the heat transfer coefficient of the atmosphere in the underground repository. In this study, the heat transfer coefficient was estimated by measuring the indoor environmental factors in the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT) under forced convection. For the experiment, a heater of 5 kw capacity, 2 meters long, was inserted through the tunnel wall in the heating section of KURT in order to heat up the inside of the rock to $90^{\circ}C$, and fresh air was provided by an air supply fan connected to the outside of the tunnel. The results showed that the average air velocity in the heating section after the provision of the air from outside of the tunnel was 0.81 m/s with the Reynolds number of 310,000~340,000. The seasonal heat transfer coefficient in the heating section under forced convection was $7.68\;W/m^2{\cdot}K$ in the summer and $7.24\;W/m^2{\cdot}K$ in the winter.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.42 no.6
• /
• pp.21-30
• /
• 2014

The purpose of this study was to evaluate human thermal comfort in summer by the type of greenery in parks and to explore planning solutions to supply a comfortable thermal environment in parks. The research was conducted in three different land cover types: a park with multi-wide-canopied trees(WOODLAND), park with grass(LAWN) and park with pavement(PAV) as reference sites in Hamyang-Gun SangrimPark. Field measurements of air temperature, relative humidity and wind velocity, short-wave and long-wave radiation from six directions(east, west, north, south, upward and downward) were carried out in the summer of 2014(August 21-23 and 29-30). Mean Radiant Temperature($T_{mrt}$) absorbed by a human-biometeorological reference person was estimated from integral radiation and the calculation of angular factors. The thermal comfort index PET was calculated by Rayman software, UTCI, OUT_SET$^*$ were calculated using the UTCI Calculator and the Thermal Comfort Calculator of Richard DeDear. The results showed that the WOODLAND has the maximum cooling effect during daytime, reduced air temperatures/$T_{mrt}$ by up to $5.9^{\circ}C/35^{\circ}C$ compared to PAV and lowered heat stress values despite increasing relative humidity values and decreasing wind velocity. While the LAWN had very slight cooling effects during daytime, reduced air temperatures/$T_{mrt}$ by up to $0.9^{\circ}C/3^{\circ}C$ compared to PAV, the improvement effects of the thermal comfort index was very slight. However, during nighttime the microclimatic and radiant conditions of WOODLAND, LAWN, and PAV were similar owing to the absence of solar radiation, reduction of wind velocity and an increase in relative humidity. Because the shading and evapotranspiration effects of the WOODLAND were much greater than the evapotranspiration effects of the LAWN, it can be said that the solutions for supplying comfortable thermal environment in parks are to amplify the green volumes rather than green areas. This study was undertaken to evaluate the human thermal comfort in summer of WOODLAND/LAWN parks and to determine the improvement effects of thermal comfort index. These results can contribute to the provision better thermal comfort for park users during park planning.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.9 no.2
• /
• pp.110-122
• /
• 1999

Hot-wire anemometers are most commonly used in measuring hood capture velocities due to their accuracy and convenience. But it was questionable that the anemometers being used in the field are accurate enough for the purpose of measurements. To answer this ques tion, a calibration wind tunnel was newly devised and tested. Subsequently, 53 hot-wire anemometers being currently used in the field were tested to evaluate the accuracy of anemometers. The average error was 16.93% while the average errors in the low (0.5~5m/s) and high (5~20m/s) velocity range were 17.40% and 16.45%, respectively. Most of anemometers underestimated the true velocities. It might be due to the contamination of hot-wire, resulting in the slow heat transfer between the sensor and air flow. Astonishingly, 16 of 53 anemometers were out of order due to the malfunctioning of zero adjustment control, power supply, display panel and sensor. It is desirable to calibrate periodically and clean the sensor after using in the dirty environment.

• Journal of the Korea Organic Resources Recycling Association
• /
• v.22 no.3
• /
• pp.60-67
• /
• 2014

Exhaust system used in toilet and cooking place of high riser public house is roof fan of two basic types : natural roof ventilator and natural/forced roof ventilator. Natural/forced roof ventilator has a motor in the rotary shaft. There are many high riser public house in Korea. These buildings were not viewed as being major contributors to exhaust pollutants producted in indoor. It was because many engineers thought that exhaust in high riser building depend on stack effect. This study investigates on stack pressure determined by exterior pressure and the difference pressure control in exhaust stack used in high riser public house. This paper focuses mainly on the effect of the time interval for power supply of motor installed in roof fan with function of natural wind velocity and of exhaust air volume of toilet. It is observed there are higher exhaust efficiency than the existing natural roof ventilator.

• Journal of the korean society of oceanography
• /
• v.36 no.1
• /
• pp.19-26
• /
• 2001

The biological pump is one of the important pumping mechanisms absorbing CO$_2$ from the atmosphere into the ocean and can be quantified by estimating new production. New production in the open ocean mostly depends on the supply of nitrate from the water below the mixed layer. While nitrate is affected by many biological processes, the helium isotope ($^3$He) is inert and has very simple physical properties. Using the $^3$He flux and the relation between $^3$He and NO${_3}\;{^-}$- within the thermocline, the nitrate flux supporting new production was estimated in the southern East Sea. The average ${\delta}^3$He within the mixed layer was -14$%_o$ and -l5.4$%_o$ in the winter and autumn, respectively. Through the year excess $^3$He occurs in the mixed layer except for a slight depletion of -17$%_o$ in summer. The $^3$He flux of 13$%_o$md$^{-1}$ associated with the concentration gradient at the air-sea interface was calculated from the product of the piston velocity and the excess $^3$He. Tritium decay within the mixed layer could support only 2$%_o$md$^{-1}$ of the flux. Thus, the remaining 11$%_o$md^{-1}$ could be attributed to the flux of tritiugenic $^3$He from the water below the mixed layer. Nitrate and $^3$He were positively correlated within the thermocline layer with the slope of 0.21 ${\mu}$mol kg$^{-1}$ $%_o\;^{-1}$. The annual nitrate flux estimated from the upward flux of $^3$He and the NO$_{3}\;{^-}$-$^3$He relation was 0.8${\pm}$0.2 mol(N) m$^{-2}$yr$^{-1}$. This flux corresponds to an annual new production of 64 g(C) m$^{-2}$yr$^{-1}$, which is consistent with that in the north-west Pacific.